Federal prosecutors allege Keys provided the hacking group Anonymous with login information to access the computer system of The Tribune Co., the Times’ parent company.

According to a federal indictment handed down last month, a hacker identified only as ‘‘Sharpie’’ used information Keys supplied in an Internet chat room to alter a headline on a December 2010 Times story to reference another hacking group. Tribune also owns a Sacramento television station Keys had been fired from months earlier.

Keys has said he did not commit the crimes he is accused of. He did not respond to a request seeking comment Monday, but he did post several online messages saying Reuters had not fired him as a result of the indictment.

‘‘Just got off the phone. Reuters has fired me, effective today. Our union will be filing a grievance. More soon,’’ he tweeted to his more than 35,000 followers.

He later tweeted a copy of a ‘‘final written warning’’ he said he received from Reuters in October, which admonished Keys for mocking a Google executive from a fake Twitter account he had created, saying the action demonstrated a ‘‘serious lapse of judgment and professionalism that is unbecoming of a Reuters journalist.’’

His attorney Jay Leiderman confirmed the firing, but said he would not comment on it because the Newspaper Guild was representing him on the matter. He added that ‘‘there is an appeals process that I will have to let play out.’’

The Guild did not immediately return a phone message seeking additional details.

Reuters hired Keys in 2012 and suspended him from his New York social media job March 14. Thomson Reuters spokesman David Girardin declined to elaborate Monday on why Keys was no longer employed.

Keys is to be arraigned Tuesday in Sacramento. He is charged with one count each of conspiracy to transmit information to damage a protected computer, as well as transmitting and attempting to transmit that information.